In our patent application Ser. No. 07/889,569 filed May 28, 1992, now U.S. Pat. No. 5,327,975, it is pointed out that rotating the production tubing string respective to the sucker rod and casing string while concurrently placing the production tubing string in tension reduces the severity of wear of a curved tubing string by reducing the contact area between the tubing string and rod string. This redistribution of wear between the sucker rod string and the tubing string is very desirable for it reduces the maintenance cost of the well, and additionally reduces the cyclic working (tension changes) of the production string and thereby overcomes many problems associated with crooked wellbores. Moreover, such an arrangement provides the unexpected benefit of enhancing the protection of the sucker rod and production tubing afforded by corrosion inhibitors which is realized because the rod and tubing rubbing surfaces are continually moved away from the contact area therebetween, thereby progressively treating the entire surface of the rod and tubing string each rotation of the tubing string.
The present invention comprehends the use of the apparatus of our prior patent in a slanted borehole. The present invention sets forth an improved new tubing rotator used in conjunction with the anchor device of our prior patent, by which the production tubing string is placed in tension while being rotated from the surface, to enable a slanted borehole to be produced in accordance with the method and apparatus set forth herein.
In this patent application, the term "slanted borehole" means a wellhead axially aligned with a casing string extending at an acute angle respective to the vertical and particularly at about 7-45 degrees respective to the vertical.
The term "crooked borehole" means a drilled hole such as a wellbore formed in the ground having a longitudinal central axis that meanders away from a straight line such that the central axis exhibits a sinusoidal wave form having an amplitude that causes a rod string located within a tubing string thereof to rub against one another at several spaced apart locations.
The term "tensioned" means that the upper and lower mandrels of the rotator and anchor are forced diametrically apart to load the upper marginal terminal end of the tubing string a tension magnitude that significantly exceeds the tension produced by the static weight of the tubing string such that the lowermost marginal terminal end of the tubing string is held in a substantial magnitude of tension.
The term "anchor" means a downhole tubing anchor device or a tubing catcher device having a mechanical apparatus thereon that is selectively actuated to prevent axial movement respective to the casing string, and is improved by the addition of a rotatable mandrel connected to form part of the tubing string flow path while rotatably holding the lower end of the tubing string in tension. There may be another length of tubing string extending downhole of the mandrel.
The term "wellbore" means a hole drilled into the ground such as a borehole or a well.
The term "cased hole" or casing means a casing string or other means associated with at least the upper end of a borehole by which the tubing rotator can be supported from close proximity of the surface.
The term "rod" means a polish rod, a rod string, a sucker rod string, a rotating shaft, as well as any rotatable or reciprocatory member extending down through a tubing string for actuating a downhole pump means for producing a well.